A mother and her child were hit and killed by a train in front of horrified rush-hour commuters at a suburban London station today.

The woman is said to have leapt onto the tracks, dragging her young son with her, and lain down seconds before a train pulled into Riddlesdown station near Purley at 8.29am.

Emergency services rushed to the scene after commuters and staff dialled 999 but the pair were declared dead at the scene.

Commuters told how they saw fellow travellers crying and in shock. The station was closed as the Metropolitan Police launched an investigation.

The tragedy caused major delays for commuters and replacement bus services had to be provided to and from a number of south London stations.

A rail worker, who did not want to be named, said he spoke to the driver afterwards and added: “He told me she dragged the kid with her as she jumped in front of the train. He is pretty shaken up, as you can imagine.”

The train, the 7.34am Uckfield to London Bridge service, was not due to stop at the suburban station and was travelling at about 50mph.

Police said the death of the child, thought to be two or three years old, is expected to be treated as a homicide.

Commuter Paul Camlett, 38, said: “I had just arrived when the station master rounded everyone up and ordered them off the platform. Everybody was at first oblivious to what had happened but then a woman screamed, ‘There’s a body on the track’.

“I’m at the office now but I really can’t work. I’m in shock. People were crying. They were in complete shock. The woman who screamed couldn’t speak afterwards.”

Police were this morning trying to trace relatives of the victims, who are believed to have lived locally.

Detective Chief Inspector Simon Taylor, who is investigating the tragedy, said: “Our thoughts remain with the family and friends of the woman and child involved.

“Officers are continuing to work to establish the full circumstances surrounding the incident, although early indications show that no one else was believed to have been involved.

“A file will now be prepared for the coroner.”

British Transport Police said: “Our officers were called to Riddlesdown station this morning after a report that a woman and a child had been struck by a train.

“Medics from the London Ambulance Service also attended but the woman and child were declared dead at the scene. The station has been temporarily closed while we deal with this.

“Inquiries are going on to establish the circumstances and a file will be prepared for the coroner.” Southern Rail said services between Sanderstead and Oxted were severely disrupted and shuttle buses were running on a number of routes.

In 2005 Navjeet Sidhu, 27, jumped in front of a Heathrow Express train at Southall clutching her five-year-old daughter and 23-month-old son. All three died instantly.

Anyone with information about the deaths today is asked to contact the British Transport Police on Freephone 0800 40 50 40.

Samaritans provide support to people in distress. They can be contacted on 08457 90 90 90